One of the main differences between Canada and the United States is the presence of relatively successful "third parties" in Canada.

The two main parties in Canadian politics have been the Liberals (roughly corresponding to the post-1930s U.S. Democrats) and the Conservatives (roughly corresponding to twentieth-century U.S. Republicans – although rather more moderate). The Liberals in Canada were, between 1896 to 2004, considerably more electorally successful in the Canadian polity than the U.S. Democrats in America. (Ironically, in this 2011 Canadian federal election, the Liberals fell to third party status, winning only 34 of 308 seats.) The Conservatives had changed their name to "Progressive Conservative" already in 1942. One of the ostensible reasons for the name change was to attract the support of a popular third party of the Western Canadian provinces – the Progressives.

In earlier years, there had also been such ephemeral protest parties as the UFO (United Farmers of Ontario). The Communist Party of Canada had famously won a seat in the federal Parliament in the 1940s. The federal-level Christian Heritage Party, the provincial-level Family Coalition Party in Ontario, and the Libertarian Party, have never won a sitting member in the legislatures for which they have run.

The most prominent of the Canadian third parties was probably the Co-operative Commonwealth Federation, renamed as the New Democratic Party in 1961. There was also the Social Credit Party (based loosely on the ideas of C. H. Douglas), which arose both in Western Canada and in Quebec – where it had a Quebec-nationalist focus. The founder of the Reform Party, Preston Manning, was the son of the longtime Alberta Social Credit Premier, Ernest C. Manning, and the accusation was sometimes made that the Reform Party were "re-tread Socreds".

The Reform Party (co-founded in 1987 by Preston Manning) transformed itself into the Canadian Alliance (officially called the Canadian Reform-Conservative Alliance) as a result of the so-called "United Alternative" process of 1998-2000. The Canadian Alliance then merged with the federal Progressive Conservative party in December 2003, renamed together as the Conservative Party. In Canada, only this federal-level party calls itself "Conservative" without the adjective – among the various provincial wings (where they exist) the name "Progressive Conservative" has been retained. The Conservative Party won 166 seats in the 2011 federal election. (One seat has been lost by the Conservatives after a recount.)

According to some observers, the triumph of the Conservative Party in 2011 is a belated triumph for Preston Manning. In the 1980s, the P.C. party was mostly hostile to so-called "small-c conservatism". Manning's Reform Party certainly divided the broader "right/centre-right/centre" vote, but it could be argued it introduced a salutary clarification into Canadian politics.

The re-unification of the CA and P.C. parties could only occur after Joe Clark (who had briefly been Prime Minister in 1979-1980, and the leader of the federal P.C.s from 1976-1983 and again in 1998-2003) left the leadership of the federal P.C.s. Joe Clark appeared to have played the role of a "spoiler" of possibly successful centre-right initiatives to the bitter twilight of his career.

But, after the merger in December 2003, the "vote-splitting" was definitely over, and, under Stephen Harper, the Conservative Party became seriously competitive. While some have argued that the Conservatives might have won a majority already in 2004, it may be supposed that Harper had some work to do to establish his credibility with the Canadian public. He won a minority government in 2006, a strengthened minority in 2008, and finally a strong parliamentary majority in 2011. It remains to be seen, however, whether Harper will choose to shred conservative principles in pursuit of an ephemeral popularity, or whether we will see some real conservatism at work in the next few years in Canada. That, one supposes, will be the ultimate test of whether this really is a belated triumph for Preston Manning.